The present invention relates to a sensor chip and a method for manufacturing a sensor chip.
Integrated fabrication techniques such as, for example, CMOS processing may be applied not only to manufacture electronic circuits but also to manufacture sensors, also denoted as sensor chips in the following. In such sensor chips, a sensor structure may be built in or on a substrate, such as a semiconductor substrate, and may or may not be integrated with associated electronic circuitry on the same chip.
In EP 1 236 038 B1, a capacitive sensor chip is disclosed containing multiple electrode elements structured on an oxide layer covering a substrate. The electrode elements are covered by insulating material which subsequently is etched. However, while the electrode elements may serve as an etch stop to the etching process, etching the insulating material in gaps between the electrode elements may only be controllable by defining the etching time upfront. This may result in varying depths etched into the insulating material. It was observed that the resulting etch depth may vary across a wafer e.g. with deeper etching results in the centre of the wafer than at its periphery. It was also observed that the resulting etch depth may vary from wafer to wafer.
In particular, when the gaps between the electrode elements will be filled by a measuring material acting, for example, as a dielectric layer between the respective electrode elements for capacitive measurements, a varying volume of the measuring material may impact the measurement results which effect may only be compensated by increased efforts in calibrating such sensor chips.